Medium and heavy-duty trucks and tractors frequently utilize a suspension system installed between the truck frame and the driver's cab to absorb shock and dampen vibrations, thereby enhancing driver comfort. As shown in FIGS. 1, 2 and 3, a prior art cab suspension system, generally designated 10, includes bushings 12 that pivotally attach the front 14 of a cab 16 to frame elements 18, 20 of an associated frame 22. The bushings 12 provide flexible attachment while controlling fore and aft movement of cab 16 relative to the frame 22. The rear 24 of the cab is attached by a system including one or more shock absorbers 26, 28, a panhard rod 30, one or more air springs 32, 34, and an air control valve 36.
The shock absorbers 26, 28 dampen vertical motion between the cab 16 and frame 22 while a transverse link or panhard rod 30 resists lateral motion. The air springs 32, 34 support the rear 24 of the cab 16. The air control valve 36 is mounted on a transverse support 38, includes a linkage 40 connected to cab rear 24, and is responsive to changes in the vertical distance between the frame 22 and cab rear. The air control valve 36 is connected to a source (not shown) of pressurized air and to the air springs 32, 34 and adjusts the air pressure in the air springs for changing cab loads.
A disadvantage with such prior art systems is that they are overly complex, relatively expensive and occupy a relatively large amount of space beneath the cab and between the rails of the associated truck or tractor. Accordingly, there is a need for a truck cab suspension system that minimizes the components required and increases the clearance beneath the cab and between the tractor frame rails, while providing lateral support and shock-damping functions. There is also a need for a truck cab suspension system whose shock and vibration damping characteristics can be varied to optimize rider comfort.